Method and apparatus for making coated metal



July 22, 1941.

M. SCHON METHOD AND APPARATUS FOR IAKING COATED METAL Filed June 28,1937 mbm/ Patented July 22, 1941 TES I einen METHD AND APPARATUS FORMAKING CUATED :METAL Matthew Schon, Baltimore, Md., assigner to CrownCork & Seal Company, Inc., Baltimore, Md., a corporation of New YorkApplication `lune 28, 1937, Serial No. 150,858

d Claims.

This invention is an improved method and apparatus for treating metalparticularly strip metal, such as hot rolled band or strip steel, eitherfor the manufacture of so-called Bright finished sheet for use, as such,in the fabrication of metallic articles or for application of a coating,such as tin.

Heretofore, in the manufacture of Bright finished sheet, for example, ithas been the practice to subject the same to at least two pickling bathtreatments for removing oxide coating and foreign matter, one precedinga cold rolling operation and another following annealing.

An object of the invention is to provide;` a method and apparatus forcold rolling `and annealing metal, which eliminates conventionalpickling. This latter has long presented difficulties but no suitableplant practice has been lhere` tofore advanced. Among the objections topickling are the difficulties ofremoving all ofthe acid, blistering andbrittleness, due to occluded hydrogen, difficulty inl controlling theacid solutions with resultant burning of the metal` due to overpickling,high initial expense of apparatus installation, cost of upkeep,rapiddepreciation of equipment Aand metal loss which averages 2%.

Numerous attempts have been made to overcome the foregoing and otherobjections to the treatment of the metal by baths of acid, such assulphuric acid, but until the present invention there has been nosuccessful commercial operation in which pickling has lbeen altogethereliminated.

In carrying out 4the invention, the metal is cleaned as by an abradingtreatment is followed by cold rolling and then by annealing in anonoxidizing atmosphere. With this procedure, not only is the initialpickling step avoided, but the usual white pickle following annealing isunnec essary, and the metal may be cut to sheet form or coiled, asdesired, although it is preferred to subject the same to a, skin passfollowing the annealing.

It has been found that sheet metal produced by such procedure, and inthe absence of pickling baths, has a high resistance to oxidation andrust, and is unusually suitable for coating, for example with tin, andsuch coatings may be made considerably thinner than customarily foundnecessary where pickling treatments are used. `For example, inaccordance with the present invention, a substantial reduction in theamount of tin per base box ispossible, and satisfactory coatings areobtained with the use of 1.1 lbs. of tin per .base box as compared toprevious procedure requiring at least 11/2 lbs. per base box.

Moreover, instead of a metal loss of approximately 2%, it has been foundpracticable, under the method of the present invention, to reduce theloss to less than 1/2 of 1%. By a simple control of the force, character(grain size and kind, e. g. cast iron or steel shot) and volume of theabrading streams in each unit, as well as the time of treatment therein,the loss of metal is negligible as compared to the loss resulting frompickling baths of acid which attack the base I metal ,beneath the oxidelm which it removes.

sheet to form Vtin plate or other coated metal.

In this connection, the invention may be practicedupon various metals,and is not limited to steel strip or bands, and the coating metal may beother than tin. The invention is particularly useful in the making ofBright finished sheet or tin plate, but, as will be appreciated, it isnot restricted to the manufacture of these articles.

From an examination of the flow sheet, it will ,be observed that thecustomary pickle used preliminary to the cold rolling operation iseliminated, as Well as the conventional White pickle rey sorted tofollowing the annealing step. These pickling treatments are unnecessary,and the objections and difficulties incident thereto are avoided byabrasively removing the oxide simultaneously from opposite sides of amoving strip which is thereafter subjected to the usual cold rollingoperation, and then annealed in a furnace under conditions which willprevent formation of oxide lm.

To illustrate the invention, and to describe a' preferred embodiment, Sindicates a coil of hot rolled strip or band steel which is supplied inthe usual manner from the mill, preferably in the form of coils weighingapproximately three tons. Such strips or bands have a surface coating ofoxide which normally is removed by a so-called continuous pickler.

In the drawing, the strip or band S is passed from the uncoiler Athrough a conventional stitcher B by means of pinch rolls C and, then,the oxide film upon the strip is removed by subjecting the strip tocleaning units such as the wheel-abrader units D. The strip isthereafter passed successively through a shearing apparatus F forshearing the strip into lengths vto provide suitable transferable coils,then through the customary scrubber and dryer G, through an oiler HThereafter, the coils in which the strip has al thickness of about .062to .100 inch are uncoiled .at J and passed through a conventional coldrolling mill K to reduce the thickness to substantially any guagedesired and recoiled as shown at L. 'Ihe c'oils are then passed from theuncoiler M through a welder N and the sheared ends thereof are weldedtogether to form a continuous strip. From the welder N, the continuousstrip is passed through a suitable electrolytic cleaner to a recoilingdevice P.

At the recoller P, the welds are cut out so that the strip will beformed into suitable transferable coils. These coils are uncoiled at Q,and the lengths are welded together at R. to form a continuous stripwhich is continuously travelled through a bright annealing furnace orother furnace T and annealed in an inert atmosphere. For-the usual typeof hot rolled band or strip treated in accordance with this invention,as just described, the annealing furnace will preferably have atemperature of between 1100 F. and 1250 F. and the atmosphere mayconsist of hydrogen. carbon monoxide, or nitrogen. A preferableatmosphere is one consisting of 6 1/2% carbon dioxide, 13.2% carbonmonoxide, '7.4 to 11% hydrogen, and .02% or less of oxygen. Bycontinuously travelling the strip through the annealing furnace at thetemperature described, and in an inert atmosphere, no opportunity foroxide to form on the surfaces is permitted and the bright hard-polishedsurfaces of the strip are not only preserved, .but they are actuallyimproved. The strip is cooled in the annealing step to a temperature atwhich oxidation is inhibited, e. g., below 250 F. After the annealingoperation, the strip is recoiled as shown at U and may be given asuitable skin pass as shown at V.

Heretofore, following the annealing treatment, it has been customary toclean the sheet by means of a white pickle. 'Ihe annealing operation inthe present method is conducted under conditions to prevent oxidation;it therefore improves the surfaces of the sheet and a cleaning orpickling treatment is not required.

The steel strip or so-called Bright finished sheet produced inaccordance with the method thus far described is useful for manypurposes. For example, in the manufacture of tin plate, or other metalcoated plate, the strip is uncoiled as shown at W. subjected to aconventional flying shear X, and severed into sheets or stripe Y ofsuitable length and width for tinning.`

It is to be understood, of course, that the metal strip or Bright nishedsheet may be continuously passed through a tinning apparatus.

Where the strips or sheets Y are to be coated with a metal, for example,tin, conventional coating practice is resorted to and the strips areiirst held in the usual water bosh Ti from which they are passed throughthe tinning machine T2 for producing tin plate T3.

As heretofore explained, a thinner coating of tin may be utilizedwithout impairing the eiliciency of the tin plate and affording a verysubstantial saving.

I claim:

1. 'I'he process of of bright annealed strip steel which comprisescold-rolling a continuous length of strip steel, thereafter annealingthe strip steel under conditions to produce a bright anneal whilepreserving the bright hard polished surfaces of the strip, andthereafter coiling the strip from the annealing furnace. f

2. The process of preparing continuous lengths of bright annealed stripsteel which comprises reducing the gauge of the metal by cold-rolling acontinuous length of strip steel, annealing the strip steel underconditions to produce a bright lanneal while preserving the bright hardpolished f surfaces of the strip, and thereafter coiling the strip fromthe annealing furnace.

3. The process of preparing continuous lengths of bright annealed stripsteel which comprises reducing the gauge of the metal by cold-rolling acontinuous length of strip steel, annealing the strip steel underconditions to produce a bright anneal while preserving the bright hardpolished surfaces of the strip, giving the strip a skin pass, and thencontinuously tinning the uncut strip.

4. The process of preparing continuous lengths of bright annealed stripsteel which comprises reducing the gauge of the metal by cold-rolling acontinuous length of strip steel, coiling the cold-rolled steel,annealing the strip steel under conditions to produce a bright annealwhile preserving the bright hard polished surfaces of the strip, coilingthe strip from the annealing furnace. giving the strip a skin pass,coiling the strip and then continuously tinning the uncut strip.

MATTEW SCHON.

preparing continuous lengths

